1. Field of the Invention
The present invention relates to a projection exposing apparatus and a projection exposing method which forms, on a wafer, a precise pattern that is required to manufacture a large scale integrated circuit (LSI).
2. Description of the Related Art
FIG. 37 illustrates an optical system of a conventional projection exposing apparatus. In the projection exposing apparatus, a fly-eye lens 13 and a mirror 12 are disposed in front of a light source 11 which serves as a lamp house. An aperture member 14 is disposed in front of the fly-eye lens 13, the aperture member 14 having a circular aperture 14a formed the central portion thereof. Further, an exposing mask 18, on which a desired pattern is formed, is disposed in of the aperture member 14 with a blind 15 for determining an exposing range, converging lenses 16a, 16b, 16c, and a mirror 17 between the mask 18 and the aperture member 14. A wafer 20, which is a substrate be exposed to light, is disposed in front of the mask 18 with projection lens systems 19a, 19b and a projection lens pupil 22 between the mask 18 and the wafer 20.
Light beams supplied from the light source 10 reach the fly-eye lens 13 by way of the mirror 12, the light beams being then distributed to respective lenses 13a that constitute the fly-eye lens 13. The light beams, passed through the respective lenses 13a, are passed through the aperture portion 14a, the converging lens 16a, the blind 15, the converging lens 16b, the mirror 17 and the converging lens 16c so that all of the mask is irradiated with the light beams. Therefore, light beams, passed through the respective lenses 13a of the fly-eye lens 13, are superimposed on one another on the surface of the mask 18, and therefore, uniform irradiation is achieved. The light beams, passed through the mask 18 as described above, are passed through the projection lens system 22 composed of the projection lens 19a, the pupil 19b and a lens 19c, so that the light beams reach the wafer 20. As a result, a precise circuit pattern is printed on a resist film on the surface of the wafer 20.
FIGS. 38 to 45 respectively are views which further schematically illustrate the conventional projection exposing apparatus shown in FIG. 37 and its modifications for various purposes. The corresponding elements are given the same or corresponding reference numerals. The structures shown in FIGS. 38 to 45 comprise the following elements that are arranged individually: a first aperture 14 so irradiated by the light source 11 (see FIG. 37) as to be a second flight source surface, a photo-mask 18 having a precise pattern and an optical image 23 on a wafer 20. However, the structures commonly comprise the following elements: a blind surface 15 for determining the region to be exposed to the irradiation light beams, a second aperture 21 formed in the mirror 17 shown in FIG. 37 and serving as a third light source surface, and a projection optical system 22 that images diffracted light beams passed from a photo-mask 18 on an exposing substrate 20 to project a circuit pattern 23.
In the projection exposing apparatus shown in FIG. 38, the first aperture 14 irradiated by the light source (see FIG. 37) forms usual irradiation light beams, the photo-mask 18 is a Levenson-type phase-shift mask, and the pattern 18a is a precise pattern. In the projection exposing apparatus shown in FIG. 38, light beam L passed through the first aperture 14, which is the second light source surface, is passed through the blind surface 15 and the second aperture 21 so that the photo-mask 18 is irradiated with the light beam L. Since the photo-mask 18 is the Levenson-type phase-shift mask, no 0-order diffracted light beam is generated but .+-.1-order diffracted light beams L1 and L-1 are generated. Further, the angle of diffraction is relatively small. The diffracted light beams are passed through the pupil of the projection optical system 22, and are incident on the wafer 20 at a relatively small angle, causing an optical image 23a to be formed. Therefore, both resolution and the depth of focus are large enough such that they are twice those of the projection exposing apparatus shown in FIG. 39, causing a satisfactory practicality to be realized.
In the projection exposing apparatus shown in FIG. 39, the first aperture 14 forms usual irradiation light beams, and the photo-mask 18 is a usual mask having a precise pattern 18b. In the projection exposing apparatus shown in FIG. 39, light beam L passed from the first aperture, which is the second light source surface, is passed through the blind 15 and the second aperture 21 so that the photo-mask 18 is irradiated with the light beam L. Since the pattern of the photo-mask 18 is formed precisely, diffracted light beams L1 and L-1 are diffracted while respectively making large angles. The diffracted light beams L1 and L-1 are passed through the periphery of the pupil of the projection optical system 22, and incident on the wafer 20 at relatively large angles so that an optical image 23b is formed. Therefore, the resultant depth of focus and the resolution are unsatisfactory, causing a problem to arise in practicality.
In the projection exposing apparatus shown in FIG. 40, the first aperture 14 forms usual irradiation light beams, and the photo-mask 18 is a usual mask having a coarse pattern 18c. In the projection exposing apparatus shown in FIG. 40, light beam L passed from the first aperture 14, which is the second light source surface, is passed through the blind 15 and the second aperture 21 so that the photo-mask 18 is irradiated with the light beam L. Since the pattern 18c of the photo-mask 18 is formed coarsely, the diffracted light beams L1 and L-1 respectively make small angles. The diffracted light beams L1 and L-1 are passed through the central portion of the pupil of the projection optical system 22, and are incident on the wafer 20 at relatively small angles from the wafer 20. As a result, an optical image 23c is formed. Therefore, satisfactory depth of focus and resolution can be realized, and therefore, the apparatus shown in FIG. 40 can be used practicably.
In the projection exposing apparatus shown in FIG. 41, the first aperture 14 forms usual irradiation light beams, and the photo-mask 18 is a usual mask having isolated pattern 18d which is formed regardless of the pattern size. In the projection exposing apparatus shown in FIG. 41, light beam L passed from the first aperture, which is the second light source surface, is passed through the blind surface 15 and the second aperture 21 so that the photo-mask 18 is irradiated with the light beam L. Since the photo-mask 18 is an isolated pattern, no optical image can be obtained on the pupil surface of the projection optical system 22 but a Gaussian-distributed diffracted light beam LG is obtained. As a result, an optical image 23d is formed on the wafer 20. The depth of focus and the resolution, which are determined depending upon the spread of the diffracted light beam G, are satisfactory.
As described above, the usual irradiation causes a problem when the usual mask having the precise pattern as shown in FIG. 39 is used. However, use of each of the masks having the patterns as shown in FIGS. 38, 40 and 41 enables a practical exposure to be performed.
In the projection exposing apparatus shown in FIG. 42, the first aperture 14 irradiated with the light source 11 (see FIG. 37) has a light-shielding member 24 to form deformed irradiation light beams. The photo-mask 18 is a Levenson-type phase shift mask having the pattern 18a formed into a precise pattern. In the projection exposing apparatus shown in FIG. 42, light beam L passed from the first aperture 14, which is the second light source surface, is passed through the blind surface 15 and the second aperture 21, which is the third light source surface, so that the photo-mask 18 is diagonally irradiated with the light beam L. Since the photo-mask 18 is a Levenson-type phase shift mask, no 0-order light beam is generated but .+-.1-order diffracted light beams are generated. The +1-order diffracted light beam L1 is blocked by the pupil of the projection optical system 22, while only the -1-order diffracted light beam L-1 is passed through the pupil and reaches the wafer 20. However, the fact, that only the -1-order diffracted light beam L-1 reaches the wafer 20, causes no interference of the diffracted light beams to occur. As a result, the optical image 23a cannot be formed, and therefore, the foregoing structure cannot be used as a practical apparatus.
In the projection exposing apparatus shown in FIG. 43, the first aperture 14 forms deformed irradiation light beams, and the photo-mask 18 is a usual mask having the precise pattern 18b. In the projection exposing apparatus shown in FIG. 43, light beam L passed from the first aperture, which is the second light source surface, is passed through the blind 15 and the second aperture 21, which is the third light source surface, so that the photo-mask 18 is diagonally irradiated with the light beam L that has a certain incidental angle. Since the pattern 23b of the photo-mask 18 is formed precisely, the diffracted light beams are diffracted while making a large angle. Therefore, +1-order diffracted light L1 is blocked by the pupil of the projection optical system 22, while 0-order diffracted light beam L0 and -1-order diffracted light beam L-1 are passed through the periphery of the pupil to be incident on the wafer 20, causing an optical image to be formed on the wafer 20. Since the incidental angles (the effective incidental angles) of the 0-order and -1-order diffracted light beams on the wafer 20 are small, excellent depth of focus and resolution can be obtained. Therefore, a satisfactorily practical apparatus can be realized.
In the projection exposing apparatus shown in FIG. 44, the first aperture 14 forms deformed irradiation light beams, and the photo-mask 18 is a usual mask having the coarse pattern 18c. In the projection exposing apparatus shown in FIG. 44, light beams passed from the first aperture 14, which is the second light source surface, are passed through the blind surface 15 and the second aperture 21 while making a certain angle, the second aperture 21 being the third light source surface. The +1-order diffracted light beam is passed through the periphery of the pupil of the projection optical system 22, while the 0-order diffracted light beam and the -1-order diffracted light beams are passed through the central portion of the pupil and are incident on the wafer to form an optical image on the wafer 20. Since the light beams which are incident on the wafer 20 include the +1-order diffracted light beam, a large effective incidental angle is made, and therefore, the depth of focus and the resolution are reduced. As a result, the foregoing apparatus cannot be used practically.
In the projection exposing apparatus shown in FIG. 45, the first aperture 14 forms deformed irradiation light beams, and the photo-mask 18 is a usual mask having an isolated pattern 18d. In the projection exposing apparatus shown in FIG. 45, the light beams passed from the first aperture 14, which is the second light source surface, are passed through the blind 15 and the second aperture 21 while making a certain angle, the second aperture 21 being the third light source surface. Thus, the photo-mask 18 is diagonally irradiated with the light beam while making a certain incidental angle from the photo-mask 18. Since the pattern of the photo-mask 18 is an isolated pattern, no optical image is formed on the pupil surface of the projection optical system 22 but Gaussian-distributed diffracted light beams are obtained. The depth of focus and the resolution are determined depending upon the spread of the foregoing diffracted light beams. Since the most intense portion of the distributed light beams is deviated from the central portion and widened in the periphery, the effective incidental angle is enlarged. Therefore, the resultant depth of focus and the resolution are too small to cause the apparatus shown in FIG. 45 to be used practically.
As described above, the deformed light beam irradiation enables adequate exposure when the usual mask having the precise pattern shown in FIG. 43 is used. However, the deformed light beam irradiation cannot be used preferably when masks having the patterns shown in FIGS. 42, 44 and 45 are used.
As described above, the conventional projection exposing apparatus encounters a problem that adequate exposure using a precise pattern cannot be performed with the usual irradiation and exposure using a coarse pattern cannot be performed adequately with the deformed light beam irradiation. Therefore, in order to perform both exposure of a precise pattern and exposure of a coarse pattern in one conventional projection and exposing apparatus, the first aperture and the photo-mask must be changed to convert the usual irradiation to the deformed light beam irradiation while also changing the size and the shape of the pupil.